Flexible blowbottles comprising a thermoplastic material and used for containing pharmaceuticals, foodstuffs, cosmetics and the like have been widely known conventionally to the extent that no further description here is necessary.
In general, the body portion of such blowbottles deforms when a plate for printing is pressed to their surface due to their flexibility, it is extremely difficult to use direct printing to indicate the contents of the bottle and the like.
Therefore, the conventional method has been to apply a positive pressure to the inside of the bottle and to achieve a balance between the positive pressure and the printing pressure so that the shape of the bottle is maintained when direct printing is performed thereon.
However, as shown in FIG. 9, in the case of a blowbag, when the sectional shape of the body portion is flat, and when it is comprised of a thermoplastic material having a the ratio of bending elasticity of between 500-10000 kg/cm.sup.2, the application of a positive pressure to the inside of the blowbag flexibly deforms the body portion 1 of the blowbag when printing is performed to that surface using a transfer roller 7, and it is difficult to maintain the required shape of the blowbag. As a result, it is extremely difficult to balance the printing pressure and the positive pressure, slippage occurs when there is printing and it is extremely difficult to have suitable printing.
In light of these problems, the present invention has as an object the provision of a blowbag manufacturing method which supports the blowbag body portion by a pressing surface of a pressing jig, and which is in close contact with an opposing wall of a blowbag so that slippage during printing of this upper surface of a body portion in this status of close contact is completely prevented, and so that even in the case of a flexible blowbag comprising a thermoplastic material having a ratio of bending elasticity of between 500-10000 kg/cm.sup.2, it is possible for the body portion to have highly accurate printing by a transfer roller.